1. Field of the Invention
The invention relates to coffee makers.
The invention relates in particular to automatic-drip coffee makers.
2. Description of Prior Art
In conventional electric automatic-drip coffee makers, water is poured into a reservoir and is heated. Hot water is pumped on to coffee grounds in a filter basket to drip into an open topped carafe. The coffee makers normally brew coffee at 190.degree. F. to 200.degree. F. and keep the coffee at that temperature by means of a hot plate beneath the carafe. Dials or sensors may be provided to let the user adjust the temperature of the coffee in the carafe. It is believed that coffee aroma and flavor will deteriorate if the carafe sits on the warm plate for some time due to continuous reheating at the bottom of the carafe and contact with air at the top of the carafe. The main benefit of using a conventional coffee maker construction with a glass carafe and a warm plate is its low cost advantage as a single heater can be employed. However, this kind of construction will usually have the problem of a too low a brewing temperature, significant heat loss through the surface of the glass carafe, continuous reheating the coffee at adjacent the bottom of the carafe, contact with cold air at the top and also an unstable warm plate temperature due to power cycling of the heater underneath.
One design solution has been proposed which employs a dual heater system, a high power vertical heater for water heating and a lower power heater underneath the warm plate. This aims to maintain a more stable warm plate temperature.
In some coffee makers, the coffee brews in a thermal carafe, using either a glass vacuum flask or stainless steel vacuum flask. A tightly fitted lid is usually present to prevent cooler air from entering the carafe. The coffee is therefore never exposed to the air and the carafe does not sit on a hot plate. Using the thermal carafe can improve some of the drawbacks of the conventional construction, because higher coffee temperature can be obtained by using a vertical heater construction. There is no need for reheating of the coffee so that a better flavor can be maintained, and there is no contact with cold air due to using an air-tight lid. But disadvantages include a lack of visibility of the coffee remaining inside the carafe, and a more bulky size for the same capacity. Also, the coffee does not stay hot continuously inside the thermal carafe, and there can be no coffee temperature adjustment inside the thermal carafe by applying external heat from a hot plate, for example. The relative cost of the thermal carafe itself is significantly higher.